Summary Neuronal ceroid lipofuscinoses (NCLs), also known as Batten disease, constitute a group of the most common neurodegenerative lysosomal storage disorders (LSDs) without an effective treatment. Mutations in >13 different genes (called CLNs) underlie pathogenesis of various types of NCLs. The infantile NCL (INCL) is one of the most devastating neurodegenerative LSDs caused by mutations in the CLN1 gene, which encodes palmitoyl-protein thioesterase-1 (PPT1). PPT1 is a lysosomal thioesterase that depalmitoylates S-acylated proteins facilitating their degradation by lysosomal hydrolases. The deficiency of PPT1 prevents degradation of S-acylated proteins (constituents of ceroid) causing accumulation of ceroid in lysosomes, which leads to INCL. There are several pathological features (e.g. elevated lysosomal pH, accumulation of intracellular autofluorescent material, GRODs, seizures and short life span) that are common to all NCLs. These features prompted us to investigate whether there are common pathogenic mechanisms shared by all NCLs. We have previously reported that cathepsin D (CD)-deficiency is a common pathogenic link between congenital NCL (CNCL), caused by mutations in the CLN10 gene encoding cathepsin D (CD), and INCL caused by mutations in the CLN1 gene encoding PPT1. Thus, in both INCL (CLN1-disease) and CNCL (CLN10-disease) lysosomal accumulation of ceroid contributes to pathogenesis. During the past year, we found that in Cln1-/- mice,which mimic INCL, Cln10/CD is overexpressed in the brain but the maturation of pro-CD to enzymatically active-CD in lysosome was impaired. During the past year we sought to determine the cause of impaired lysosomal acidification in INCL using Cln1-/- mice as a model. Defective lysosomal acidification contributes to virtually all lysosomal storage disorders (LSDs) and to common neurodegenerative diseases like Alzheimer's and Parkinson's. Despite its fundamental importance, the mechanism(s) underlying this defect remains unclear. The v-ATPase, a multisubunit protein complex composed of cytosolic V1-sector and lysosomal membrane-anchored V0-sector, regulates lysosomal acidification. We found that in brain tissues of Cln1-/- mice, which mimic INCL, reduced v-ATPase activity correlated with elevated lysosomal pH. Moreover, v-ATPase subunit a1 of the V0 sector (V0a1) requires palmitoylation for interacting with adaptor protein-2 (AP-2) and AP-3, respectively, for trafficking to the lysosomal membrane. Unexpectedly, we found that in Ppt1-deficient Cln1-/- mice V0a1 transport defect misrouted it to the plasma membrane instead of its normal location on lysosomal membrane. Notably, treatment of Cln1-/- mice with a thioesterase (Ppt1)-mimetic small molecule, NtBuHA, ameliorated this defect. Our findings reveal an unanticipated role of Cln1 in regulating lysosomal targeting of V0a1 and suggest that varying factors adversely affecting v-ATPase function dysregulate lysosomal acidification in other LSDs and common neurodegenerative diseases. As part of a project studying the treatment benefits of a combination of cysteamine bitartrate and N-acetyl cysteine, we made serial measurements of patients' brain volumes with MR imaging. Ten patients with infantile neuronal ceroid lipofuscinosis participating in a treatment/follow-up study underwent brain MR imaging that included high-resolution T1-weighted images. After manual placement of a mask delineating the surface of the brain, a maximum-likelihood classifier was applied to determine total brain volume, further subdivided as cerebrum, cerebellum, brain stem, and thalamus. Patients' brain volumes were compared with those of a healthy population. Major subdivisions of the brain followed similar trajectories with different timing. The cerebrum demonstrated early, rapid volume loss and may never have been normal postnatally. The thalamus dropped out of the normal range around 6 months of age; the cerebellum, around 2 years of age; and the brain stem, around 3 years of age. Rapid cerebral volume loss was expected on the basis of previous qualitative reports. Because our study did not include a nontreatment arm and because progression of brain volumes in INCL has not been previously quantified. However, the level of quantitative detail in this study allows it to serve as a reference for evaluation of future therapeutic interventions. A US Patent (US 20140148513 A1), entitled Small molecule therapeutic compounds targeting thioesterase deficiency disorders and methods of using the same has been granted. Previously, we and others have previously reported that in Cln1-/- mice, which mimic INCL, there is progressive decline in synaptic vesicle (SV) pool-size at the nerve terminals with age. However, the mechanism underlying this defect was not clearly understood. Dynamin1 is a small GTPase that plays critical roles in recycling and regeneration of fresh SVs. We found that this defect is partly due to impairment of exocytosis and endocytosis at the presynaptic membrane required to regenerate SVs. We sought to determine whether in Cln1-/- mice inactivation of dynamin-1 contributes to SV-recycling defect. We observed a significantly higher level of phosphorylated dynamin-1 in Cln1-/- mice. Phosphorylation inactivates this GTPase, which may lead to impaired SV-recycling and progressive decline in SV-pool size in these mice. Ongoing investigations are attempting to delineate the mechanism by which dynamin-1 phosphorylation is increased in Cln1-/- mice. Since neurotransmission is an important element in neurodegenerative diseases, our study may uncover the mechanism of this defect and allow the development of novel therapeutic strategies for INCL.